1. Field of the Invention
The present invention relates to an epoxy resin curing composition comprising an epoxy compound and a novel amide compound modified with a carboxyl-containing acrylonitrilebutadiene copolymer.
2. Description of the Prior Art
Up to this time, polyamines, modified polyamines, amideamines, alicyclic polyamines, modified aromatic amines and Mannich bases of polyamines have been practically used as a room-temperature curing agent for epoxy resins. These curing agents disadvantageously give cured resins exhibiting poor peel strength and insufficient adhesion to various plastics, flexible vinyl chloride resins and rubbers, though having an excellent adhesion (tension shear strength) to metals and mortars.
Various studies on an improvement in adhesion to such adherends have been made up to this time. For example, a process comprising adding nylon 66 to an epoxy resin and a process comprising adding various rubbers, thermoplastics or polyurethane rubbers to an epoxy resin and/or the above curing agent or reacting the former with the latter have been proposed. However, though the cured resin compositions prepared by these processes exhibit improved adhesion, they exhibit such a poor resistance to water and chemicals disadvantageously that they can be used only in limited fields.
Recently, amide compounds comprising adducts of a terminal carboxyl-containing acrylonitrile-butadiene copolymer with N-aminoethylpiperazine have been developed and used as a curing agent for epoxy resins to give cured epoxy resin compositions having improved adhesion and improved flexibility. However, they are problematic because of high viscosity, high load and high cost and have a disadvantage in that remaining unreacted N-aminoethylpiperazine brings about toxicity to the skin and poor resistance to chemicals, particularly to acids.
Japanese Patent Laid-Open No. 179268/1982 discloses an epoxy resin adhesive composition excellent in peel strength which contains a polyamideamine containing a diene copolymer component in its molecule. Further, it is described in one Example thereof that the use of an adduct of a carboxyl-terminated acrylonitrile-butadiene copolymer with polyamideamine gave an adhesive composition having improved adhesion, particularly peel strength. However, though this adhesive composition exhibits improved adhesion as compared with the composition containing polyamides according to the prior art, the acid resistance thereof is so poor that it can be used only in limited fields. The reason of this poor acid resistance is thought to be as follows: The amide-forming reaction between a carboxyl-containing acrylonitrile-butadiene copolymer and a primary amine is restricted by the steric hindrance of the nitrile group of the copolymer to the carboxyl group thereof, so that amine salts of --COOH/NH.sub.2 remain in the reaction product, thus remarkably lowering the characteristics, particularly acid resistance, of the epoxy resin composition cured with the product.
Therefore, development of an epoxy resin curing composition, the peel strength of which is improved without detriment to water resistance, chemical resistance, mechanical strength and the like has been expected.